Unlike the right cavities of the heart, for which it is sufficient to implant endocardial leads via the right peripheral venous network, the implantation of permanent leads into a left heart cavity involves significant operating risks, e.g., passing bubbles to the cerebral vascular network located downstream of the left ventricle. For this reason, when it is desirable to stimulate the left cavity, a stimulation catheter is introduced via the coronary network, rather than in the cavity. The lead is equipped with an electrode to be applied against the wall of the epicardium and to steer it toward the left ventricle or left atrium, as appropriate.
The introduction of such a lead is made through the coronary sinus opening into the right atrium, thus by an endocardial approach. It is then guided and driven along the network of coronary veins to the chosen stimulation site. This intervention is particularly difficult given the peculiarities of the venous system and of its access paths, particularly because of the valves and tortuosities, and because of the gradual reduction in diameter of the vessel as the lead progresses in the selected coronary vein. Furthermore, the position of the stimulation site, a good electrical contact of the electrode with the tissue of the epicardium, and the correct orientation of the stimulating electrode, are particularly important aspects to consider when implanting the lead into the heart cavity.
For example, in the case of a “multisite” pacemaker, preferably for the interventricular resynchronization, the two points of stimulation of the left ventricle/right ventricle should be as far apart as possible, so as to optimize the resynchronization of all the cardiac chambers. It is also important to reduce the risk of phrenic nerve stimulation during or after implantation.
These aspects must be evaluated not only at the time of implantation, but it is also necessary that the quality and accuracy of the contact in the site of stimulation are not significantly changed in the medium term, for example, because of patient movements such as changes in posture, wide movements of arms and heavy breathing.
EP 0993840 A1 and its US counterpart U.S. Pat. No. 6,385,492 (ELA Medical, now known as Sorin CRM S.A.S) describe a pre-shaped lead adapted for implantation in the coronary venous system. The lead head includes a sector electrode and has a double curvature to ensure a self-orientation of the lead tip so that the sector electrode is directed toward the epicardium when the lead head has reached its final position. This pre-shaped lead is used in combination with a stylet that allows the operator to more or less reform the curvature during implantation to facilitate the progression of the lead head to the heart in the peripheral venous system, then the search of the coronary sinus, and finally, the progression of the lead head in the coronary system to the selected site of stimulation. A commercial embodiment of this type of lead is marketed by Sorin CRM under the Situs LV lead brand.
The pre-shaped leads are sometimes difficult to advance, as they move along according to the principle of least energy. At an applied force to insert the lead or torque to rotate the lead, the lead moves or rotates in the direction and orientation where the least energy is required. In addition, their extraction capacity remains unknown, with a risk of damaging the coronary network veins during explantation of the lead.
Finally, one of the classical drawbacks of conventional pre-shaped leads is their tendency to restore to their original shape (due to the principle of least energy), which causes postoperative micro-displacements affecting the quality of the thresholds and/or the resynchronization.
Another problem is the difficulty in finding a good stimulation site, to achieve a good electrical contact of the electrode against the tissue of the epicardium, and maintain this contact despite variations or various solicitations in time. It is also essential to avoid any phrenic stimulation, both during and after the implantation.
To overcome these difficulties, it was proposed to have multiple electrodes along the lead body to increase the chances of an acceptable compromise, possibly by giving the lead body a particular lead conformation. The operator can thus choose, among the various electrodes present on the lead body, the one providing the best electrical efficiency. On the other hand, to reduce risks of variation in the medium term of the electrical contact and of later phrenic stimulation, manufacturers have introduced the concept of “electronic repositioning” to direct or redirect the electric field between different electrodes placed along the stimulation lead of the left ventricle and/or with one of the electrodes of the stimulation lead from the right ventricle, in order to avoid a re-intervention. The counterpart of this solution is a growing complexity of the structure of the lead, an increase in the number of electrodes causing an increase in the number of components and electrical wiring, or the use of multiplexing circuits for selecting from among the various electrodes on the same lead.
The WO-A-02/04062 A2 (Medtronic) describes a technique of “telescopic approach” usually used in various applications (notably in angioplasty) to make a cannulation either of the ostium of the coronary sinus or a lateral vein. This technique is based on the use of two catheters, one inserted inside the other, with longitudinal and circular relative movements possible, the movements being controlled by the physician on the proximal side. It is theoretically possible to orient the termination of the inner catheter to direct the termination of its distal curve to the epicardium but, as in the targeted application the catheter is “partitioned/adjusted” in the venous network, the expected equilibrium position generates a lot of counter torque that must be opposed. As a result, the expected equilibrium position is relatively unstable.
Several phenomena complicate the task of the physician, for example, the fact that the fine control of the orientation is subject to the quality of the torque transmission, which is particularly linked to: (i) the diameter of the catheter, which is expected to be as small as possible and (ii) the length of the catheter, which is in the order of 70 cm. The small diameter and long length of the catheter are unfavorable for good control. This fine control is also perturbed by the cardiac movements which render the equilibrium of the system unstable, as the screwing operation can occur over a duration in the order of ten seconds. Keeping the catheter in place while performing the screwing operation may require two operators.
The implantation of a catheter is consequently “operator dependent” because it is difficult to obtain a secured positioning of the anchoring helical screw of the catheter.
The anchoring helical screw needs to be oriented in an appropriate direction during screwing. Indeed, the fixation qualities of a screw lead are broadly known in the field of cardiac pacing leads, but this technique is not used as of today in the coronary sinus because the risks of dissection of the coronary sinus is too high. Nevertheless, the fixation remains the main problem when implanting the left ventricular pacing leads via the coronary sinus.
The U.S. Pat. No. 5,837,007 (Pacesetter) proposes a solution to this problem by means of a retractable screw. But this technique is complex, because it requires at least three components (up to six components) with the use of a soluble element or a component having mechanical characteristics that significantly change after impregnation by corporeal fluids. Furthermore, the torque transmission is performed via a stylet that directly engages the screw. This requires an additional accessory and complicates the operation, which is already complex and delicate to implement.
The present invention aims to remedy the above difficulties, in particular by overcoming problems associated with the use of leads equipped with multiple electrodes.